Drawing on basic psychological needs theory (BPNT; Deci & Ryan, 2000), the aim of this thesis was to investigate the influence that pupils' autonomy, competence and relatedness may have upon their personal and academic functioning at school. The purpose was to provide new conceptual insights into BPNT within young adolescents' schools and to identify practically viable interventions that could enhance educational practise. Specifically, this thesis addresses two methodological vacancies within BPNT research and two practically driven investigations. The first methodological consideration involved a person-centred examination that identified distinct pupil profiles based on differences in their psychological need satisfaction composition. Hierarchal cluster analysis revealed four distinct pupil groups. Pupils reporting the highest satisfaction across the three needs displayed the highest levels of well-being, autonomous motivation, teacher rated performance, and the least ill-being. These person-centred findings emphasise the necessity for the satisfaction of all three psychological needs, as well as highlighting specific need deficits that some pupils may experience in classrooms. The second methodological consideration explored how the satisfaction of each psychological need may predict changes in school attainment patterns. Hierarchal growth modelling revealed that higher pupil competence satisfaction was a driving stimulus for temporal attainment increases across the school year, whereas higher pupil relatedness satisfaction buffered against the summer decay of school grades following the summer vacation. These findings offer unique insights into the dynamic nature of school attainment. From a practical perspective, the thesis explored if the candid frustration of different psychological needs underpins active and passive types of classroom disengagement. Structural equation modelling demonstrated the frustration of pupil competence uniquely explained passive disengagement via reduced subjective vitality, whereas experiences of autonomy frustration underpinned both active and passive disengagement but not via subjective vitality. All three disengaging processes were found as a consequence of perceived psychologically controlling teaching. Finally, the thesis explored the feasibility of conducting a novel pupil-focused intervention to enhance pupils' perceptual awareness of their own psychological needs. Using a pupil completed diary-log as a methodology, a two week pilot and focus group discussion highlighted practical issues and recommendations for the potential implementation of a future intervention. These findings indicated that the diary-log may need to be in the form of an electronic application and would need to be combined with existing need supportive sessions. Overall, the thesis findings add to existing knowledge by indicating how pupils' psychological needs may enhance or diminish their academic and psychological development at school. The findings allude to the interplay between the three needs within school contexts and provide insights into the unique role the different psychological needs may have on school attainment and disengagement. The findings also suggest there may be scope to advance existing teacher-focused BPNT interventions by helping pupils become more active in their own experiences of psychological need satisfaction.